KR102084905B1 - Electroless plating process - Google Patents

Abstract

In the case where the nickel plated film and the gold plated film are formed in order on the surface of the copper material, the purpose of the present invention is to provide an electroless plating process in which the film thickness of the nickel plated film can be reduced and a film having excellent mounting characteristics can be obtained. do. In order to solve the above problems, an electroless plating process of sequentially forming a nickel plating film and a gold plating film on the surface of a copper material by an electroless plating method, and a step of forming a nickel plating film on the surface of a copper material by an electroless strike plating method. And forming a gold plated film according to a reduced electroless plating method.

Description

Electroless plating process

The present invention relates to an electroless plating process for forming a gold plated film on the surface of a copper material by an electroless plating method.

In recent years, while the demand for high functionalization and multifunctionalization of electronic devices has increased, electronic circuit boards such as resin substrates, ceramic substrates, and wafer substrates used in such electronic devices have been required to be light and small in size. In order to cope with this light and small size, high-density mounting is required, and thus a surface treatment technique capable of realizing high-density mounting is required. In the technical field of electronic circuit boards, a mounting technique using solder or wire bonding has been established as a technique for joining mounting components.

In order to ensure the connection reliability at the time of mounting, the plating process is performed as a surface treatment to the wiring pad which is the mounting part of the circuit pattern on an electronic circuit board. For example, a nickel plating film and a gold plating film are formed in order on the circuit pattern formed of metals, such as low resistance copper, by plating process. Hereinafter, the film in which the nickel plating film and the gold plating film were formed in order is described as "Ni / Au film." The nickel plated film is formed to prevent diffusion of copper into the gold plated film, and the gold plated film is formed to obtain good mounting characteristics.

Moreover, the technique of forming a palladium film between a nickel plating film and a gold plating film is also known. Hereinafter, the film in which the nickel plating film, the palladium plating film, and the gold plating film were formed in order is described as "Ni / Pd / Au film." The palladium film is formed to prevent diffusion of nickel into the gold plated film during the heat treatment of the plated substrate. When the palladium film is formed on the nickel plated film, the nickel plated film can be thinned.

As said plating process, although electrolytic plating process is mainstream, the electroless plating process is applied about the thing which cannot cope with an electrolytic plating process.

Conventionally, as an electroless plating process for forming a Ni / Pd / Au film on the surface of copper, for example, Patent Document 1 discloses a degreasing step (step (hereinafter, "S") with respect to a copper material as shown in FIG. 11) and etching (S12), giving a palladium catalyst to the surface of the copper material (S14), then electroless nickel (Ni) plating (S15), electroless palladium (Pd) plating (S16) and electroless It is disclosed to perform gold plating (Au) plating (S17). Although it is not described in patent document 1, it is common to perform a dismert (S13) between etching (S12) and a palladium catalyst provision process (S14). The palladium catalyzing treatment (S14) is usually essential in order to proceed with nickel precipitation during electroless nickel plating (S15).

In the electroless nickel plating disclosed in Patent Document 1 (S15), 22.5 g / L of nickel sulfate hexahydrate (5 g / L in terms of nickel), sodium hypophosphite as a reducing agent, malic acid and succinic acid as complexing agents, As the stabilizer, an electroless nickel plating solution containing lead salts, bismuth salts, sulfur compounds and the like and having a pH of 4.6 and a bath temperature of 60 to 90 ° C is used. It is also possible to use dimethylamine borane instead of sodium hypophosphite as the reducing agent. Then, a nickel plating film having a thickness of 0.1 to 15 µm is formed by electroless nickel plating (S15), a palladium plating film having a thickness of 0.001 to 2 µm is formed by electroless palladium plating (S16), and an electroless gold plating ( According to S17), a gold plated film having a thickness of 0.001 to 1 µm is formed.

In order to realize higher density mounting in the Ni / Au film or the Ni / Pd / Au film, it is preferable to further thin the nickel plated film.

Japanese Patent Publication No. 2008-174774

However, when the above-mentioned electroless nickel plating (S15) forms a very thin nickel plated film having a film thickness of, for example, 0.01 μm or less, the coating is insufficient, and fine grooves (holes) are formed on the surface of the nickel plated film. It may occur. When the subsequent electroless gold plating S17 is performed, the grooves may corrode to generate through holes penetrating the nickel plating film. This phenomenon is called "nickel local corrosion phenomenon." In this case, there is a problem that excellent mounting characteristics cannot be obtained in the Ni / Au film or the Ni / Pd / Au film.

An object of the present invention is an electroless plating process in which when the nickel plated film and the gold plated film are sequentially formed on the surface of a copper material, the film thickness of the nickel plated film can be reduced and a film having excellent mounting characteristics can be obtained. The purpose is to provide.

The electroless plating process according to the present invention is an electroless plating process in which a nickel plating film and a gold plating film are sequentially formed on the surface of a copper material by an electroless plating method, and a nickel plating film is formed on the surface of a copper material by an electroless strike plating method. Forming step; And forming a gold plated film according to a reduced electroless plating method.

In the electroless plating process according to the present invention, the electroless strike plating method, 0.002 ~ 1g / L water-soluble nickel salt in terms of nickel; Carboxylic acids or salts thereof; And at least one reducing agent selected from the group consisting of dimethylamine borane, trimethylamine borane, hydrazine and hydrazine derivatives, wherein the pH is 6-10 and the bath temperature is adjusted to 20-55 ° C. using an electroless nickel strike plating solution. In this case, the copper material is preferably immersed in the electroless nickel strike plating solution.

The electroless nickel strike plating solution is prepared by mixing and stirring the water-soluble nickel salt, the carboxylic acid or its salt, and water to prepare an aqueous solution containing a nickel complex, and then mixing and stirring the reducing agent in the aqueous solution. Is preferably.

In the electroless plating process according to the present invention, the step of forming the nickel plated film is preferably to form a nickel plated film having a film thickness of 0.005 ~ 0.3μm.

In addition, the electroless plating process according to the present invention is to form a nickel plated film, a palladium plated film and a gold plated film in order on the surface of the copper material, between the step of forming the nickel plated film and the process of forming the gold plated film It is preferable to provide a process for forming a palladium plating film according to the reduction type electroless plating method.

In the electroless plating process according to the present invention, by adopting the electroless strike plating method, a nickel plating film can be directly formed on the surface of the copper material even without performing the palladium catalyzed treatment (S14) performed in the conventional electroless plating process. Can be. Moreover, even if the film thickness is thin, the surface of the copper material can be reliably covered, and a nickel plated film excellent in adhesion to the copper material can be formed. Therefore, according to the electroless plating process which concerns on this invention, thin film formation of a nickel plating film can be implement | achieved. In the electroless plating process according to the present invention, by adopting a reduced electroless plating method, a gold plated film or a palladium plating film can be formed without eluting the metal of the film formed before. Therefore, according to the electroless plating process which concerns on this invention, the Ni / Au film or Ni / Pd / Au film excellent in the mounting characteristic can be obtained.

1 is a flowchart showing an electroless plating process of the present embodiment.
FIG. 2 is an SEM photograph of the nickel plated film obtained in the electroless plating process of Example 1. FIG.
3 is an SEM photograph of the nickel plated film obtained in the electroless plating process of Comparative Example 1. FIG.
4 is an SEM photograph of the nickel plated film obtained in the electroless plating process of Comparative Example 2. FIG.
5 is a graph showing the results of low potential electrolysis of the nickel plated film obtained in the electroless plating processes of Example 1 and Comparative Example 1. FIG.
6 is a graph showing solder spreadability of the Ni / Pd / Au film obtained in the electroless plating processes of Example 1 and Comparative Example 1. FIG.
7 is a graph showing the solder ball shear strength of the Ni / Pd / Au coatings obtained in the electroless plating processes of Example 1 and Comparative Example 1. FIG.
8 is a graph showing wire bonding strengths of Ni / Pd / Au films obtained in the electroless plating processes of Example 1 and Comparative Example 1. FIG.
9 is a graph showing a gold wire breaking mode of the Ni / Pd / Au film obtained in the electroless plating processes of Example 1 and Comparative Example 1. FIG.
10 is a flow chart illustrating a prior art electroless plating process.

Next, an embodiment of the electroless plating process according to the present invention will be described. The electroless plating process of this embodiment is a nickel plating film and a gold plating film according to the electroless plating method on the surface of copper materials, such as an electrode and wiring provided in the surface of insulating base materials, such as a resin substrate, a ceramic substrate, and a wafer substrate, for example. It is an electroless plating process that forms in order. Specifically, it is an electroless plating process including a step of forming a nickel plated film on the surface of a copper material by an electroless strike plating method and a step of forming a gold plated film by a reduced type electroless plating method. Hereinafter, an electroless plating process for forming a Ni / Pd / Au film on the surface of the copper material by forming a nickel plating film, a palladium plating film and a gold plating film on the surface of the copper material in order will be described.

In the electroless plating process of this embodiment, as shown in FIG. 1, first, as a pretreatment before forming a nickel plating film, a degreasing process (S1), an etching process (S2), and a dimmer process (S3) are performed. Thereafter, a nickel plating film is formed on the surface of the copper material by the electroless nickel (Ni) strike plating step (S4). Subsequently, a palladium plating film is formed by an electroless palladium (Pd) plating process (S5), and a gold plating film is formed by an electroless gold (Au) plating process (S6). After each process, a water washing process is performed. It is preferable to perform a water washing process three times.

1. Degreasing process (S1)

In the degreasing step (S1), the fat or oil adhering to the surface of the copper material is removed by dipping the copper material in an acidic solution.

2. Etching Process (S2)

In the etching step (S2), the copper oxide film formed on the surface of the copper material is removed by immersing the copper material subjected to the degreasing step (S1) in an etching solution such as persulfate, hydrogen peroxide, or thiol.

3. Dismute process (S3)

In the dimmer process S3, the smut adhering to the surface of the copper material is removed by immersing the copper material subjected to the etching step S2 in, for example, 10% sulfuric acid.

4. Electroless Nickel Strike Plating Process (S4)

In the electroless nickel strike plating step (S4), a nickel plating film is formed on the surface of the copper material pretreated by the electroless strike plating method. The electroless strike plating method is carried out by immersing the copper material subjected to the discharging step (S3) in an electroless nickel strike plating solution.

Electroless Nickel Strike Plating Solution ：

The electroless nickel strike plating solution is a water-soluble nickel salt; Carboxylic acids or salts thereof; And at least one reducing agent selected from the group consisting of dimethylamine borane, trimethylamine borane, hydrazine, and hydrazine derivatives. In this specification, "one or more types" means only 1 type may be sufficient as 2 or more types.

Water Soluble Nickel Salt:

As a water-soluble nickel salt used for an electroless nickel strike plating liquid, organic acid nickel, such as nickel sulfate, nickel chloride, nickel carbonate, nickel acetate, nickel hypophosphite, nickel sulfamate, nickel citrate, is mentioned, for example. These can be used independently and can also be used in combination of 2 or more type. In the present invention, it is most preferable to use nickel sulfate hexahydrate as the water-soluble nickel salt.

It is preferable that an electroless nickel strike plating liquid is 0.002-1 g / L in nickel conversion content of water-soluble nickel salt. This is not more than 1/5 of the nickel concentration of 5 g / L of the electroless nickel plating solution used in the electroless nickel plating (S15) of the prior art electroless plating process, and the concentration is very low. When the electroless nickel strike plating solution has a nickel equivalent content of the water-soluble nickel salt in the above range, the electroless strike plating method can be realized to form a nickel plating film directly on the surface of the copper material to which the palladium catalyst is not applied.

If the nickel conversion content of the water-soluble nickel salt is less than 0.002 g / L, the precipitation rate is excessively slowed. Therefore, in order to obtain a nickel plated film having a desired film thickness, it is necessary to lengthen the immersion time, and the industrial productivity cannot be satisfied. Not desirable On the other hand, when the nickel conversion content of water-soluble nickel salt exceeds 1 g / L, precipitation rate will become excessively fast and a nickel plating film with a uniform surface may not be obtained, and it is unpreferable. The nickel conversion content of the water-soluble nickel salt is more preferably in the range of 0.01 to 0.5 g / L, and most preferably in the range of 0.03 to 0.1 g / L.

Carboxylic acid or its salts:

Electroless nickel strike plating solutions include carboxylic acids or salts thereof. These act as complexing agents or pH adjusters. As the carboxylic acid, for example, monocarboxylic acid (formic acid, acetic acid, propionic acid, butyric acid, etc.), dicarboxylic acid (oxalic acid, malonic acid, succinic acid, gluconic acid, adipic acid, fumaric acid, maleic acid, succinic acid, etc.), tricarboxylic acid (aconic acid) Etc.), hydroxycarboxylic acids (citric acid, lactic acid, malic acid), aromatic carboxylic acids (benzoic acid, phthalic acid, salicylic acid, etc.), oxocarboxylic acids (pyruvic acid, etc.) and amino acids (arginine, asparagine, aspartic acid, cysteine, glutamic acid, glycine, etc.) One or more types selected can be used.

It is preferable to use carboxylic acid or its salt in the range whose total is 0.5-5 g / L, and the range of 0.8-2 g / L is more preferable. The electroless nickel strike plating solution of the present embodiment has a lower nickel content compared to the electroless nickel plating solution used in the electroless nickel plating (S15) of the electroless plating process of the prior art, so that the content of carboxylic acid or its salt is lowered. Setting. Although carboxylic acid or its salt also depends on the kind, when content is less than 0.5 g / L, it is unpreferable since complex formation of the nickel ion in an electroless nickel strike plating liquid may become inadequate and precipitation may occur. On the other hand, even if the content of the carboxylic acid or its salt exceeds 5 g / L, not only a special effect is obtained, but also a waste of resources is not preferable.

reducing agent:

The electroless nickel strike plating solution contains at least one reducing agent selected from the group consisting of dimethylamine borane, trimethylamine borane, hydrazine and hydrazine derivatives. By using these substances as the reducing agent in the electroless nickel strike plating solution, nickel deposition on the surface of the copper material to which the palladium catalyst is not provided can be realized. From the viewpoint of safety to the human body, dimethylamine borane and trimethylamine borane are more preferable.

It is preferable to use a reducing agent in the range of 2-10 g / L, and the range of 4-8 g / L is more preferable. If the content of the reducing agent is less than 2 g / L, a sufficient reducing action is not obtained, and nickel precipitation on the copper surface may not proceed, which is not preferable. When the content of the reducing agent exceeds 10 g / L, nickel is abnormally precipitated on surfaces other than copper (the surface of the insulating substrate) or bath decomposition of the electroless nickel strike plating solution may occur, which is not preferable.

The electroless nickel strike plating solution is prepared by mixing the above components with water, stirring and dissolving them. The electroless nickel strike plating solution is prepared by mixing and stirring the water-soluble nickel salt, the carboxylic acid or its salt, and water to prepare an aqueous solution containing a nickel complex, and then mixing and stirring the reducing agent in the aqueous solution. desirable. In the electroless nickel strike plating solution prepared in this way, the nickel complex can be stably present for a long time, and excellent bath stability can be obtained.

The electroless nickel strike plating solution may contain components such as sulfate, boric acid, chloride salt, etc. in addition to the above components.

pH ：

The electroless nickel strike plating liquid is preferably adjusted to a neutral region having a pH of 6 to 10. If the pH is less than 6, the nickel deposition rate is lowered and the film forming property of the nickel plated film is lowered, which may cause holes or grooves on the surface of the nickel plated film, which is not preferable. On the other hand, when the pH exceeds 10, the nickel deposition rate is excessively high, which makes it difficult to control the film thickness of the nickel plated film, or the crystal state of precipitated nickel cannot be densified, which is undesirable.

Bath temperature ：

It is preferable that bath temperature of an electroless nickel strike plating liquid is adjusted to 20-55 degreeC. This is a value lower than the bath temperature of 60-90 degreeC of the electroless nickel plating liquid used by the electroless nickel plating (S15) of a prior art. If bath temperature is less than 20 degreeC, nickel deposition rate will fall and the film-forming property of a nickel plating film will fall, and a hole or a groove | channel may arise in the surface of a nickel plating film, or nickel may not precipitate, which is unpreferable. On the other hand, when bath temperature exceeds 55 degreeC, the bath stability of an electroless nickel strike plating liquid will fall, and an electroless strike plating method may not be implement | achieved, and it is unpreferable.

Film thickness ：

The film thickness of the nickel plating film is adjusted by the immersion time in the electroless nickel strike plating solution. It is preferable that the film thickness of a nickel plating film is as thin as possible in the range which can prevent the diffusion of copper, and it is preferable that it is 0.005-0.3 micrometer. If the thickness of the nickel plated film is less than 0.005 μm, the coating on the surface of the copper material is insufficient, resulting in minute grooves on the surface of the nickel plated film. As a result, nickel local corrosion phenomenon occurs when the subsequent electroless gold plating process (S6) is performed. This is undesirable, since copper or nickel may diffuse onto the surface of the gold plated film. On the other hand, it is also possible to form a nickel plated film having a thickness of more than 0.3 μm, but it is not preferable because the flexibility of the nickel plated film is not only degraded, but also waste of resources.

According to the electroless nickel strike plating process (S4) of this embodiment, the thinning of the nickel plating film which was difficult in the conventional electroless nickel plating (S15) can be realized, and the nickel plating film whose film thickness is 0.005-0.3 micrometers is used. You can get it. Moreover, in order to realize thin film while ensuring favorable mounting characteristics, it is more preferable that the film thickness of the nickel plating film formed by an electroless nickel strike plating process (S4) is 0.007-0.1 micrometer.

In the electroless nickel strike plating step (S4) of the present embodiment, at least one substance selected from the group consisting of dimethylamine borane, trimethylamine borane, hydrazine and hydrazine derivatives contained in the electroless nickel strike plating solution acts as a reducing agent. Nickel can be deposited on the surface of the copper material to which the palladium catalyst is not provided. And the nickel content of an electroless nickel strike plating liquid is low, pH is 6-10, and bath temperature is adjusted to 20-55 degreeC. As a result, the deposition rate of nickel is slowed, the electroless strike plating method is realized, and a nickel plating film can be directly formed on the surface of the copper material. At this time, since the deposition rate of nickel is slow, nickel can be uniformly deposited on the surface of the copper material. As a result, even if the film thickness is uniform, a nickel plated film which reliably covers the surface of the copper material is formed. can do. The obtained nickel plating film is excellent in adhesiveness with respect to a copper material, and is excellent in the barrier property which prevents the diffusion of copper compared with the nickel plating film obtained by the conventional electroless plating process.

On the other hand, in the electroless nickel plating (S15) performed by the electroless plating process of the prior art, palladium provided to the surface of a copper material by a palladium catalyst provision process (S14) acts as a catalyst, and nickel precipitation advances. Therefore, the area | region to which the palladium catalyst was given and the area | region not provided to the copper material surface generate | occur | produce a deviation in the film thickness of the nickel plating film formed, and it is difficult to obtain a nickel plating film of uniform film thickness. In addition, the electroless nickel plating solution used in the electroless nickel plating (S15) has a high nickel content and a high bath temperature, so the deposition rate of nickel is high, so that a nickel plating film excellent in adhesion to the copper material is hardly obtained.

According to the electroless nickel strike plating process (S4) of this embodiment, when dimethylamine borane and trimethylamine borane are used as a reducing agent, the nickel plating film which consists of an alloy of nickel and boron (nickel-boron alloy) can be obtained. . This nickel plating film is a nickel plating film which is extremely low in boron content (for example, 0.1% or less), and consists of pure nickel substantially. In addition, when hydrazine and a hydrazine derivative are used as a reducing agent, the nickel plating film which consists of pure nickel can be obtained.

In addition, in the electroless nickel strike plating step (S4), the content of the water-soluble nickel salt in the electroless nickel strike plating solution is as low as 0.002 to 1 g / L. Therefore, bath decomposition can be prevented from occurring without using a stabilizer such as lead salt or bismuth salt used in the electroless nickel plating (S15) of the electroless plating process of the prior art. In addition, since the electroless nickel strike plating solution does not contain stabilizers such as lead salt and bismuth salt, a nickel plating film containing no heavy metal such as lead or bismuth can be obtained.

5. Electroless Palladium Plating Process (S5)

In an electroless palladium plating process (S5), a palladium plating film is formed in the surface of the said nickel plating film by the reduction type electroless plating method. When the palladium film is formed by the substitutional electroless plating method, a nickel local corrosion phenomenon, that is, nickel may be eluted and a through hole penetrating the nickel plated film may be formed, so a reduced electroless plating method is employed.

A well-known thing can be used as a reduced type electroless palladium plating liquid used for an electroless palladium plating process (S5). For example, reduced electroless containing 0.001-0.1 mol / L of palladium compounds, 0.05-5 mol / L of amine compounds, 0.01-0.1 mol / L of inorganic sulfur compounds, 0.05-1.0 mol / L of hypophosphorous acid or hypophosphorous acid compounds A palladium plating liquid can be used. Alternatively, a reduced electroless palladium plating solution containing 0.001 to 0.1 mol / L of formic acid or formic acid compound may be used instead of the hypophosphorous acid or hypophosphorous acid compound.

In the electroless palladium plating step (S5), by employing a reduced electroless plating method, it is possible to prevent elution of nickel from the nickel plating film when forming the palladium plating film. And in the electroless plating process of this embodiment, since the nickel plating film formed by the electroless nickel strike plating process (S4) is uniform in film thickness and excellent in smoothness, according to the electroless palladium plating process (S5), it is uniform. A palladium plating film having a film thickness can be formed.

6. Electroless Gold Plating Process (S6)

In the electroless gold plating step (S6), a gold plated film is formed on the surface of the palladium plating film by a reduction type electroless plating method. When the gold plated film is formed by the substitutional electroless plating method, palladium is eluted and a through hole penetrating the palladium plated film may be formed. Thus, a reduced electroless plating method is employed.

A well-known thing can be used as a reduced type electroless gold plating solution used for an electroless gold plating process (S6). For example, water-soluble gold compound; Citric acid or salts thereof; Ethylene diamine tetraacetic acid or its salts; Hexamethylenetetramine as a reducing agent; A reduced type electroless gold plating solution including a chain polyamine comprising an alkyl group having 3 or more carbon atoms and 3 or more amino groups can be used.

In the electroless gold plating step (S6), the elution of palladium from the palladium plating film can be prevented when the gold plating film is formed by employing the reduced electroless plating method. In the electroless plating process of the present embodiment, since the palladium plating formed by the electroless palladium plating process S4 has a uniform film thickness, the electroless gold plating process S6 has a uniform film thickness. A gold plated film can be formed.

After completion of the electroless gold plating process, it is washed with water and dried. As described above, the Ni / Pd / Au film can be formed on the surface of the copper material by performing the electroless plating process shown in FIG. 1.

In the electroless plating process of this embodiment, a nickel plating film can be directly formed in the copper material surface to which the palladium catalyst is not provided by the electroless nickel strike plating process (S4). And even if a film thickness is thin, the surface of a copper material can be reliably covered, and the nickel plating film excellent in adhesiveness with respect to a copper material, and a barrier characteristic can be formed. Therefore, the thinning of the nickel plating film can be realized.

Moreover, since the film thickness of a nickel plating film can be made thin, the Ni / Pd / Au film with a small total film thickness can be obtained. In addition, since the nickel plating film having a uniform film thickness and excellent smoothness can be obtained by the electroless nickel strike plating step (S4), the palladium plating film and the gold plating film formed thereon can also be formed with a uniform film thickness. The Ni / Pd / Au film can be formed with a small variation in the film thickness. In addition, the nickel plated film formed by the electroless strike plating method is excellent in adhesion to the copper material and excellent in barrier property to prevent copper diffusion, thereby forming a Ni / Pd / Au film having excellent mounting characteristics. can do.

In addition, the nickel plating film is thin in thickness, and unlike the nickel plating film formed by the electroless nickel plating (S15) of the prior art, it does not contain phosphorus. From this, since the nickel plating film can obtain excellent flexibility, the Ni / Pd / Au film can obtain excellent flexibility.

In addition, unlike the electroless plating process of the prior art, in the electroless plating process of this embodiment, since it is not necessary to perform a palladium catalysis provision process (S14) before an electroless nickel strike plating process (S4), the number of processes is changed. Can be reduced.

The electroless plating process of this embodiment mentioned above is a process of performing an electroless palladium plating process S5 and an electroless gold plating process S6 after an electroless nickel strike plating process S4. In the electroless plating process of this embodiment, after performing an electroless nickel strike plating process (S4) and performing an electroless gold plating process (S6) without performing an electroless palladium plating process (S5), Ni / Au coating on the surface of a copper material It may be a process of forming a.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated concretely based on an Example etc ..

Example 1

In the electroless plating process of the present Example, Ni / Pd / Au films were formed on the surface of a copper material by performing each process S1-S6 (6 steps in total) shown in FIG. The above-described degreasing step (S1), etching step (S2), and dismuting step (S3) were carried out in order, followed by electroless nickel strike plating step (S4). In the electroless nickel strike plating step (S4), the copper material was immersed in the electroless nickel strike plating solution of the following composition, and a nickel plating film was formed on the surface of the copper material. The electroless nickel strike plating solution was prepared by mixing and stirring nickel sulfate hexahydrate, DL-peracid and water to prepare an aqueous solution containing a nickel complex, followed by adding and stirring dimethylamine borane. While the copper material was immersed in the electroless nickel strike plating liquid, the electroless nickel strike plating liquid was stirred by aeration.

Electroless Nickel Strike Plating Solution

Nickel sulfate hexahydrate 0.2g / L (0.045g / L in nickel conversion)

DL-apple acid 1.0g / L

Dimethylamine borane 4.0g / L

pH 9.0

Bath temperature 50 ℃

Subsequently, an electroless palladium plating process (S5) was performed. The copper material in which the nickel plating film was formed was immersed in the reduced type electroless palladium plating liquid of the following composition, and the palladium plating film was formed in the surface of the nickel plating film.

(Reduced Electroless Palladium Plating Solution)

Palladium chloride 0.038mol / L

Ethylenediamine 0.142mol / L

Sodium formate: 0.294 mol / L

pH 6.0

Bath temperature 70 ℃

Thereafter, an electroless gold plating step (S6) was performed. The copper material in which the palladium plating film was formed was immersed in the reduction type electroless gold plating liquid of the following composition, and the gold plating film was formed in the surface of the palladium plating film. As described above, the Ni / Pd / Au film was formed on the surface of the copper material.

(Reduction type electroless gold plating amount)

Gold Potassium Cyanide 5mmol / L

Ethylenediaminetetraacetic acid dipotassium acetate 0.03mol / L

Citric acid 0.15mol / L

Hexamethylenetetramine 3mmol / L

3,3'- diamino-N-methyldipropylamine 0.02mol / L

Tallium Acetate 5mg / L

pH 8.5

Bath temperature 80 ℃

Comparative example

Comparative Example 1

The electroless plating process of this comparative example was carried out instead of the electroless nickel strike plating process (S4) except having performed palladium catalysis giving process (S14) and electroless nickel plating (S15) performed by the electroless plating process of a prior art, The Ni / Pd / Au film was formed on the surface of the copper material by performing the same procedure as in the electroless plating process of Example 1. The process of the electroless plating process of this comparative example was a total of 7 processes.

In palladium-catalyst provision process (S14), the immersed copper material was immersed in the palladium-catalyst solution containing a 30 mg / L palladium compound and sulfate ion in palladium conversion, and the palladium catalyst was provided to the surface of the copper material.

In electroless nickel plating (S15), the copper material to which the palladium catalyst was given was immersed in the electroless nickel plating liquid of the following composition.

Electroless Nickel Plating Solution

Nickel sulfate hexahydrate 22.4g / L (5g / L in nickel conversion)

DL-apple acid 15g / L

Lactic acid 18g / L

Sodium hypophosphite 30 g / L

pH 4.5

Bath temperature 80 ℃

Comparative Example 2

The electroless plating process of this comparative example was performed completely similarly to the comparative example 1 except having used the electroless nickel plating liquid of the following composition in electroless nickel plating (S15). The process of the electroless plating process of this comparative example was 7 processes in total.

Electroless Nickel Plating Solution

Nickel sulfate hexahydrate 22.4g / L (5g / L in nickel conversion)

Glycolic Acid 30g / L

Acetic acid 15 g / L

Dimethylamine borane 2.5g / L

pH 6.0

Bath temperature 60 ℃

Reference Example 1

The electroless plating process of this reference example was carried out in exactly the same manner as in Comparative Example 1 except that the palladium catalyst applying treatment (S14) was not performed before the electroless nickel plating (S15). The electroless plating process of this reference example had a total of 6 steps.

Reference Example 2

The electroless plating process of this reference example was carried out in exactly the same manner as in Comparative Example 2 except that the palladium catalyst applying treatment (S14) was not performed before the electroless nickel plating (S15).

<Evaluation>

1. Evaluation of Nickel Plating Film

First, the electroless nickel strike plating process (S4) of the electroless plating process of Example 1 is performed, or the process to the electroless nickel plating (S15) of the electroless plating processes of Comparative Examples 1 and 2 is performed. By carrying out, the nickel plating film of a film thickness of 0.01 micrometer was formed in the surface of a copper material. The following evaluation was performed about the obtained nickel plating film.

1-1. Nickel precipitation

Here, a test board was used in which 30 copper pads having a diameter of 0.45 mm were arranged in a lattice shape at intervals of 30 μm on an insulating substrate. Then, up to the electroless nickel strike plating step (S4) of the electroless plating process of Example 1, or the steps up to the electroless nickel plating (S15) of the electroless plating processes of Comparative Examples 1 and 2 are performed. The nickel plating film was formed in the surface of a copper pad by performing. On the other hand, in the electroless plating processes of Reference Example 1 and Reference Example 2, the steps up to electroless nickel plating (S15) were performed, but nickel did not precipitate at all on the surface of the copper pad, and a nickel plating film could not be formed.

The obtained nickel plating film was observed with the metal microscope (magnification 1000x), and the number of the copper pads which nickel precipitation performed normally was counted. Here, that the nickel deposition was performed normally means that the entire surface of the copper pad is covered with a nickel plating film, and the uncoated portion is not confirmed by the metal microscope. The results are shown in Table 1. The judgment criteria of the ○ mark, the △ mark, and the × mark in Table 1 are as follows.

(Circle): There are 30 copper pads which nickel deposition performed normally.

(Triangle | delta): The copper pad in which nickel precipitation was normally performed is 15-29 pieces.

X: There are 30 copper pads in which nickel did not precipitate at all.

As shown in Table 1, when comparing Comparative Example 1 and Reference Example 1 and Comparative Example 2 and Reference Example 2, the electroless nickel plating used for the electroless nickel plating of Comparative Example 1 and Comparative Example 2 (S15) In order to form a nickel plating film by a nickel plating liquid, it can be understood that palladium catalysis giving process (S14) is essential before electroless nickel plating (S15) is performed.

In addition, although electroless nickel plating (S15) of the comparative example 1 can always perform nickel precipitation normally, electroless nickel plating (S15) of the comparative example 2 may not be able to perform nickel precipitation normally, and nickel precipitation property I can understand what is falling. On the other hand, in the electroless nickel strike plating step (S4) of Example 1, it can understand that nickel precipitation can always be normally performed and it is excellent in nickel precipitation property.

1-2. Surface shape

In order to evaluate the surface form of the nickel plated film formed on the surface of the copper pad, the surface of the nickel plated film was photographed at a magnification of 5000 times and 30,000 times by scanning electron microscope (SEM) to obtain a reflection electron composition image (COMPO phase). The results are shown in FIGS. 2 to 4. FIG. 2 shows the COMPO phase of the nickel plated film obtained by the electroless nickel strike plating step (S4) of Example 1, and FIG. 3 shows the COMPO of the nickel plated film obtained by the electroless nickel plating (S15) of Comparative Example 1. FIG. A phase is shown, and FIG. 4 shows the COMPO phase of the nickel plating film obtained by the electroless nickel plating (S15) of the comparative example 2. As shown in FIG. 2 (a), 3 (a) and 4 (a) are 5000 times magnification, and FIGS. 2 (b), 3 (b) and 4 (b) are 30,000 times magnification. to be.

2 to 4, the nickel plated film obtained by the electroless nickel strike plating step (S4) of Example 1 includes the nickel plated film obtained by the electroless nickel plating (S15) of Comparative Example 1 and Comparative Example 2; In comparison, it can be confirmed that there are few black parts. The black portion shows that an element such as carbon having a small atomic number is present on the nickel plating film. From this, the nickel plating film obtained by the electroless nickel strike plating process (S4) of Example 1 compared with the nickel plating film obtained by the electroless nickel plating (S15) of Comparative Example 1 and Comparative Example 2, a defective part. It can be understood that this is a small and dense film. In addition, the nickel plating film obtained by the electroless nickel plating (S15) of the comparative example 2 has many black parts, and it can be understood that it is not a dense film with many defect parts.

In addition, nickel obtained by the electroless nickel strike plating process (S4) of Example 1 has a large unevenness | corrugation on the surface of the nickel plating film obtained by the electroless nickel plating (S15) of Comparative Example 1 and Comparative Example 2. It can be confirmed that the plated film does not have large irregularities on the surface, and only fine irregularities exist. From this, the nickel plating film obtained by the electroless nickel strike plating process (S4) of Example 1 has the smoothness compared with the nickel plating film obtained by the electroless nickel plating (S15) of Comparative Example 1 and Comparative Example 2. I can understand the excellence. In addition, it can be understood that the nickel plated film of Comparative Example 2 is inferior in smoothness due to the large number of large irregularities.

As mentioned above, according to the electroless nickel strike plating process (S4) of the electroless plating process of Example 1, compared with the electroless nickel plating (S15) of the electroless plating processes of Comparative Example 1 and Comparative Example 2, It can be understood that a nickel plated film having excellent smoothness can be obtained.

1-3. Surface Elemental Analysis

The surface elemental analysis was performed with the Auger electron spectroscopy apparatus about the nickel plating film formed in the surface of a copper pad. As mentioned above, since the nickel plating film of the comparative example 2 was inferior in performance, only the nickel plating film of Example 1 and the comparative example 1 was made into object.

The reflow process was performed three times with respect to the nickel plating film. The reflow process was performed by preheating a nickel plating film at 230 degreeC, and then heating at 250 degreeC. Then, surface element analysis was performed before the reflow treatment and after the reflow treatment to naturally cool down to room temperature. The measurement conditions of surface element analysis were acceleration voltage 10kV, probe current value 10nA, measurement diameter 50micrometer, and scanning range 30-2400 eV. The results are shown in Table 2. The numerical value of Table 2 quantifies an element from the peak intensity ratio of the obtained spectrum (unit: atomic%). -In Table 2 means that the corresponding element was not detected at all.

The nickel plated film obtained by the electroless nickel strike plating step (S4) of Example 1 was thought to contain boron derived from dimethylamine borane, but in reality it was found that boron was not substantially detected and consisted of pure nickel. . On the other hand, the nickel plating film obtained by the electroless nickel plating (S15) of the comparative example 1 consisted of the nickel-phosphorus alloy containing phosphorus derived from sodium hypophosphite, as shown in Table 2.

From Table 2, it can be understood that the nickel plating film obtained by the electroless nickel strike plating step (S4) of Example 1 is excellent in barrier performance because copper is not diffused on the surface even after the second reflow treatment. On the other hand, in the nickel plated film obtained by the electroless nickel plating (S15) of Comparative Example 1, although copper was not diffused on the surface after the first reflow treatment, copper was deposited on the surface after the second reflow treatment. It can be understood that the diffusion is poor and the barrier performance is poor.

1-4. Low potential electrolysis

Here, a nickel plated film having a thickness of 0.01 μm was formed on the surface of the copper plate by using a copper plate instead of the test board. Then, the obtained nickel plated film was subjected to low potential electrolysis at 50 mV in a 0.5% by volume sulfuric acid solution to evaluate barrier properties. The results are shown in FIG. In the figure, the horizontal axis represents electrolysis time, and the vertical axis represents current density. The increase in the current density indicates that copper was eluted from the copper material under the nickel plated film.

As shown in FIG. 5, the nickel plating film obtained by the electroless nickel strike plating process (S4) of Example 1 is compared with the nickel plating film obtained by the electroless nickel plating (S15) of Comparative Example 1, and a current density. It is understood that the barrier property is excellent because the rise of is small.

From the results of the above nickel precipitation, surface morphology, surface element analysis and low potential electrolysis, the electroless nickel strike plating process (S4) of the electroless plating process of Example 1 was performed by the electroless plating processes of Comparative Examples 1 and 2 It can be understood that a nickel plating film having excellent nickel precipitation property as well as a fine, smooth and excellent barrier performance can be obtained as compared with the electroless nickel plating (S15). In addition, the nickel plating film obtained by the electroless nickel strike plating process (S4) of the electroless plating process of Example 1 has the electroless plating of the electroless plating processes of the comparative example 1 and the comparative example 2 which have the same film thickness. It can be understood that it has the performance superior to the nickel plating film obtained by nickel plating (S15).

2. Evaluation of Ni / Pd / Au Film

Here, fine wiring of copper having a wiring width / wiring spacing (L / S) of 30 to 100 µm / 30 to 100 µm is arranged on the insulating substrate, and a copper pad having a diameter of 0.45 mm is formed in a lattice shape at intervals of 0.45 µm. The test board placed as was used. By carrying out a total of six steps of the electroless plating process of Example 1 or a total of seven steps of the electroless plating process of Comparative Example 1, the test board was subjected to Ni / Pd / on the surface of the copper material (fine wiring and pad). An Au film was formed.

In the electroless plating process of Example 1, the Ni / Pd / Au film which consists of a nickel plated film with a film thickness of 0.01 micrometer, a palladium plating film with a film thickness of 0.1 micrometer, and a gold plating film with a film thickness of 0.1 micrometer was obtained. In the electroless plating process of Comparative Example 1, a Ni / Pd / Au film formed of a nickel plated film having a thickness of 0.5 μm, a palladium plated film having a thickness of 0.1 μm, and a gold plated film having a thickness of 0.1 μm was obtained. And the following evaluation was performed about the obtained Ni / Pd / Au film.

2-1. Solder spreadability

Solder was performed on the surface of the Ni / Pd / Au film, and the solder spread test was performed after that. As the solder ball, Eco Solder (registered trademark) M770 of Senju Metal Industry Co., Ltd. was used, and the solder ball diameter (D) was 700 micrometers. Solder spread test was carried out using preliminary heating temperature of 230 degreeC and reflow temperature of 250 degreeC using the solder reflow furnace (Japan Pulse Technology Research Institute, RF-330), and AGF-780DS of Asahi Chemical Research Institute, Inc. as a flux. -AA was used. And the height H (micrometer) of the solder ball after reflow was measured, spreading ratio S was calculated by the following formula, and the maximum value, minimum value, and average value were calculated | required. Moreover, the solder spread test was similarly performed about the Ni / Pd / Au film which heat-treated for 4 hours at the temperature of 250 degreeC, before soldering. The results are shown in FIG. "No heat treatment" in FIG. 6 shows the result of the solder spread test of the Ni / Pd / Au film which was soldered without performing the heat treatment after the electroless plating process of Example 1 or Comparative Example 1, and "with heat treatment" Silver shows the result of the Ni / Pd / Au coating which soldered after performing the said heat processing following the said electroless plating process.

Spread rate (S) = (D-H) / D × 100 (%)

From FIG. 6, the Ni / Pd / Au film obtained by the electroless plating process of Example 1 was compared with the Ni / Pd / Au film obtained by the electroless plating process of Comparative Example 1 in both heat treatment and heat treatment. It can be understood that the solder spreadability is excellent. In comparison with no heat treatment and heat treatment, the Ni / Pd / Au film obtained by the electroless plating process of Example 1 was obtained by the electroless plating process of Comparative Example 1, while the difference between the average value and the minimum value was small. The average value of the Ni / Pd / Au film is greatly reduced. From this, the Ni / Pd / Au film obtained by the electroless plating process of Example 1 has a high effect of suppressing diffusion of copper or nickel into the gold plated film by heat treatment, and maintains excellent solder spreadability even when the heat treatment is performed. It can be understood that it has excellent heat resistance.

2-2. Solder ball shear strength

Solder was applied to the surface of the Ni / Pd / Au film, and then the solder ball shear strength was measured. The solder ball shear strength was measured at a shear height of 20 µm and a shear rate of 500 µm / second using a daisy ball (Series 4000) solder ball shear tester, and the maximum, minimum, and average values were determined. Moreover, the solder ball shear strength was similarly measured also about the Ni / Pd / Au film which heat-treated at the temperature of 250 degreeC for 4 hours before soldering. The results are shown in FIG. "No heat treatment" in FIG. 7 shows the solder ball shear strength of the Ni / Pd / Au film which was soldered without performing the heat treatment after the electroless plating process of Example 1 or Comparative Example 1, and with "heat treatment" After the heat treatment following the electroless plating process, the result of the soldered Ni / Pd / Au film is shown.

From Fig. 7, both of the heat treatment without heat treatment and the Ni / Pd / Au coating obtained by the electroless plating process of Example 1 were compared with the Ni / Pd / Au coating obtained by the electroless plating process of Comparative Example 1. It is understood that the numerical value itself is low, but with good solder ball shear strength. In addition, comparing the absence of heat treatment with heat treatment, the Ni / Pd / Au film obtained by the electroless plating process of Example 1 was obtained by the electroless plating process of Comparative Example 1 while the difference between the average value and the minimum value was small. In the Ni / Pd / Au film, the average value and the minimum value are greatly reduced before and after the heat treatment. From this, the Ni / Pd / Au film obtained by the electroless plating process of Example 1 was compared with the Ni / Pd / Au film obtained by the electroless plating process of Comparative Example 1, and the It can be understood that the effect of suppressing diffusion into the gold plated film is high, and excellent solder ball shear strength can be maintained even when heat treatment is performed, and thus excellent heat resistance is provided.

2-3. Wire Bonding Strength and Break Mode

After bonding a gold wire having a wire diameter of 25 μm to the surface of the Ni / Pd / Au film, the bonding strength when the gold wire was pulled with a pull tester, that is, the wire bonding strength was measured. And the maximum value, minimum value, and average value were calculated | required. Moreover, the wire bonding strength was similarly measured also about the Ni / Pd / Au film which heat-processed for 4 hours at 250 degreeC before soldering. The results are shown in FIG. Moreover, the breaking mode at the time of breaking a gold wire is shown in FIG. "No heat treatment" in FIGS. 8 and 9 shows the wire bonding strength or the breaking mode of the Ni / Pd / Au film which was soldered without performing the heat treatment after the electroless plating process of Example 1 or Comparative Example 1. "With heat treatment" has shown the result of the Ni / Pd / Au coating which soldered after performing the said heat processing following the said electroless plating process.

From Fig. 8, the Ni / Pd / Au film obtained by the electroless plating process of Example 1 was subjected to Ni / Pd / Au without heat treatment obtained by the electroless plating process of Comparative Example 1 in both without heat treatment and with heat treatment. It can be understood that it has a wire bonding strength equivalent to that of the coating. In addition, comparing the absence of heat treatment with heat treatment, the Ni / Pd / Au film obtained by the electroless plating process of Example 1 was obtained by the electroless plating process of Comparative Example 1, while the difference between the average value and the minimum value was small. The average and minimum values of the Ni / Pd / Au film are greatly reduced.

In addition, as shown in FIG. 9, in the Ni / Pd / Au film obtained by the electroless plating process of Example 1, the fracture mode when the gold wire was broken was both C mode without heat treatment and with heat treatment. . On the other hand, in the Ni / Pd / Au film obtained by the electroless plating process of Comparative Example 1, all of the heat treatment was C mode, while in heat treatment, 45% was C mode and 55% was E mode.

From these results, the Ni / Pd / Au film obtained by the electroless plating process of Example 1 was compared with the Ni / Pd / Au film obtained by the electroless plating process of Comparative Example 1, and the copper and nickel by heat treatment. It is understood that the effect of suppressing diffusion into the gold plated film is high, and even when the heat treatment is performed, the wire bonding strength and the breaking mode can be maintained, thereby providing excellent heat resistance.

The Ni / Pd / Au coating obtained by the electroless plating process of Example 1 was obtained by the electroless plating process of Comparative Example 1 from the results of the above solder spreadability, solder ball shear strength, wire bonding strength, and fracture mode. Although the film thickness of a nickel plating film is 1/50 compared with a / Pd / Au film, it can understand that it has the outstanding mounting characteristic equivalent or more. This is considered to be because the nickel plating film formed in the electroless nickel strike plating process (S4) of the electroless plating process of Example 1 is dense and smooth, and excellent in barrier performance.

As explained above, according to the electroless plating process of this invention, a Ni / Au film or a Ni / Pd / Au film can be formed in the surface of a copper material. Since the obtained nickel plating film can reliably cover the surface of a copper material even if a film thickness is thin, according to the electroless plating process of this invention, thinning of a nickel plating film can be implement | achieved. Since the obtained Ni / Au film or Ni / Pd / Au film can obtain excellent mounting characteristics even when the nickel plating film is thin, the electroless plating process of the present invention can cope with complicated wiring patterns and narrow pitch wiring. High density mounting can be realized. In addition, the obtained Ni / Au film or Ni / Pd / Au film is very suitable as a flexible substrate because the overall film thickness is thin and excellent in flexibility.

Moreover, according to the electroless plating process of this invention, since a nickel plating film can be formed, without carrying out the palladium catalyst provision process (S14) performed by the conventional electroless plating process, productivity can be improved.

Claims (5)

An electroless plating process in which a nickel plating film and a gold plating film are sequentially formed on the surface of a copper material by an electroless plating method,
Forming a nickel plating film on the surface of the copper material by an electroless strike plating method; And
And forming a gold plated film according to a reduced electroless plating method.
And said electroless nickel plating solution used for said electroless strike plating does not contain phosphorus. The method of claim 1,
The electroless strike plating method is a water-soluble nickel salt of 0.002 ~ 1g / L in terms of nickel; Carboxylic acids or salts thereof; And at least one reducing agent selected from the group consisting of dimethylamine borane, trimethylamine borane, hydrazine and hydrazine derivatives, wherein the pH is 6-10 and the bath temperature is adjusted to 20-55 ° C. using an electroless nickel strike plating solution. And immersing the copper material in the electroless nickel strike plating solution. The method of claim 2,
The electroless nickel strike plating solution is prepared by mixing and stirring the water-soluble nickel salt, the carboxylic acid or its salt, and water to prepare an aqueous solution containing a nickel complex, and then mixing and stirring the reducing agent in the aqueous solution. Electroless Plating Process. The method according to any one of claims 1 to 3,
The step of forming the nickel plating film is to form a nickel plating film having a film thickness of 0.005 ~ 0.3μm, the electroless plating process. The method according to any one of claims 1 to 3,
The electroless plating process is to form a nickel plating film, a palladium plating film and a gold plating film in order on the surface of the copper material,
And a step of forming a palladium plated film in accordance with a reduced electroless plating method between the step of forming the nickel plated film and the step of forming the gold plated film.

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